Micro Power Generation System Research Articles

Experimental investigation of the micro-power generation system based on porous burning

This study presents a micro-power generation system based on porous combustion and gasification of biomass energy. The efficient heat exchange between porous combustion-based technology and a free-piston Stirling engine generator (FPSEG) was investigated to convert biomass energy into electric energy. Alumina ceramic particles were used to build a porous medium area within a heat transfer power generation experimental platform to explore the influence of the porous medium bed height and particle diameter, as well as the effect of inlet gas conditions on the system power generation performance. Specifically, the speed of power generation of the system increased and then decreased with an increase in the height of the bed, with maximal power generation speed observed when the height of the bed was 45 mm. The change in the alumina ceramic particle diameter was not significantly related to the rising speed of the system; however, when the diameter of the alumina ceramic particles was less than 15 mm, the flame front could not be stabilized in the porous medium, indicating that a critical particle size existed in the porous medium. Increased gas intake resulted in the power generation rate of the system to first increase and then decrease. When the gas intake was 9.3 m3/h, the power generation rate of change reached 1.2 W/s.

Enhancing Thermal Performance, Exergy and Thermodynamics Efficiency of Premixed Methane/Air Micro-Planar Combustor in Micro-Thermophotovoltaic Systems

The present work numerically investigates the effect of a cavity implemented in a premixed methane/air micro-combustor on enhancing its thermal performances and thermodynamic efficiencies for micro-thermophotovoltaic applications. The 3D time-domain numerical model is first validated by comparing its predictions with the experimental data available in the literature. Then it is applied to examine the effects of the cavity dimensionless axial location (xc/L), cavity volume (Vc), the equivalence ratio ϕ and hydrogen blended ratio (α) on the temperature uniformity and enhancement of the combustor outer wall and exergy efficiency. It is found that implementing a cavity in the combustion chamber increases the outer wall mean temperature (OWMT) and the exergy efficiency up to approximately 65 K and 10%, respectively. The optimal cavity dimensionless axial location (xc/L) is set to 1/9, and the height (Hc_dims) is 1/5, respectively. However, the cavity length Lc and angle θc are found to play negligible roles on improving thermal performance. Additionally, increasing the inlet velocity leads to a higher OWMT but a low exergy efficiency, regardless of the equivalence ratio. In general, this work confirms the feasibility of applying a cavity structure to enhance energy efficiency for micro-power generation systems.

Project of Micro-hydroelectric Power Generation System – Case study

Abstract The article describes a student project of installing a micropower generation system utilizing energy from the water drained from underground coalmines. The paper contains a description of the site which is a manmade phenomenon from the anthracite mining era. The project described in the article was completed as part of the project-based learning curriculum. Students had the opportunity to work on a team and apply theoretical knowledge learned in individual courses as part of the engineering curriculum. The article also focuses on the calculation of the potential power capacity to a proposed hydropower generation system. The proposed micro-hydro system is harvesting the potential and kinetic energy of the water discharged from the water-draining tunnel. A commercially available micro-hydro turbine combined with an electric power generator was adapted for this purpose. The article also includes an analysis of the profitability of the project and the time of return on investment. The calculations are based on the current price of electricity (2021), depreciation schedule and present tax incentives (2021) to generate electricity from renewable sources. The article also includes some lessons learned from the project as well as the recommendations for future projects.

Energy conversion efficiency improvement studies on unconventional premixed micro-combustors partially inserted with porous medium

Benefited from the rapid development of composite materials, the application of micro-power generation systems with curved surface have become achievable. In order to explore thermal performances and emitter efficiency assessments of curved combustors, T- and Y-shaped micro-combustors partially inserted with porous medium (PM) are both experimentally and numerically investigated. Comparison is then made with the conventional I-shaped micro-combustor fuelled with premixed CH4/O2/Ar. The effects of: 1) the geometry shape, 2) the mass flow rate ṁ, 3) the extending depth of the flame holder, 4) the PM size and 5) its axial location have been evaluated. Results show that the radiation efficiency ηE of the double-channel micro-combustor is higher than that of the single-channel under the same working condition. PM can effectively improve the temperature uniformity of the combustor outer surface. The best thermal performance is achieved, when the extending depth of the flame holder is 2.0 mm. The T-shaped combustor is asscoaited with the highest ηE of 39.4% with a PM length of 8 mm when ṁ=4.8×10−6kg/s. This study provides a potential design for further improving the energy conversion efficiency of MTPV system.

Numerical analysis of oil injection effects in a single screw expander

The pursuit of higher efficiency for compression and micro-power generation systems has pushed the researchers to an in-depth analysis of positive displacement machines. Single-screw machines, among the others, are gaining attention in the Organic Rankine Cycle (ORC) systems as expanders, thanks to their extended maintenance intervals and compactness. The performances of such devices are strongly affected by the working conditions, and especially the presence of oil has major effects on the operability. The main advantage of adopting an oil-injected device consists in the lube sealing effect, which permits better performance (greater shaft power for assigned boundary conditions) as well as higher reliability. The choice of whether using an oil-free configuration or not is related to the working fluid cleanness, system complexity (oil separator, filters, recovery pump), flow rate and pressure ratio. In this paper, the full 3D numerical simulation of an oil-injected single-screw expander operating with R245fa refrigerant is presented. Oil is injected together with the working fluid at the inlet of the machine. Oily droplets are tracked over the admission duct to show how the oil droplets reach the inlet ports of the screw machine. Different behaviors related to different oil droplet diameters in the range of (0.5 - 50) μm are studied, for the same operating point. The proper distribution of the oil droplets on the screw inlet ports are directly related to the single screw expander performance. In addition, a particular screw position is analyzed for studying the effects of leakages on the oil injection and oil film evolution over the time.

Thermodynamic assessment of integrated biogas-based micro-power generation system

In this paper, a thermodynamic modelling of an integrated biogas (60%CH4+40%CO2) micro-power generation system for electricity generation is reported. This system involves a gas turbine cycle and organic Rankine cycle (ORC) where the wasted heat of gas turbine cycle is recovered by closed ORC. The net output power of the micro-power generation system is fixed at 1.4MW includes 1MW power generated by GT and 0.4MW by ORC. Energy and exergy assessments and related parametric studies are carried out, and parameters that influence on energy and exergy efficiency are evaluated. The performance of the system with respect to variation of design parameters such as combustion air inlet temperature, turbine inlet temperature, compressor pressure ratio, gas turbine isentropic efficiency and compressor isentropic efficiency (from the top cycle) and steam turbine inlet pressure, and condenser pressure (from bottoming cycle) is evaluated. The results reveal that by the increase of gas turbine isentropic efficiency, the outlet temperature of gas turbine decreases which incurs negative impacts on the performance of air preheater and heat exchanger, however the energy and exergy efficiency increases in the whole system. By the increase of air compressor pressure ratio, the energy and exergy of the combined cycle decreases. The exergy efficiency of ORC alters by the variation of gas turbine parameters which can be attributed to the variation of temperature discrepancy between gas turbine exhaust temperature and ORC working fluid. Both first and second law efficiency of the combined cycle increases with the enhancement of inlet pressure of ORC turbine due to the mitigation of exergy destruction in heat exchanger. The rate of power generation in ORC increases by the enhancement of ORC turbine inlet pressure, however overall exergy destruction of the cycle decreases slightly.

Design Optimization of a Micro-Combustor for Lean, Premixed Fuel-Air Mixtures

Present technology has been shifting towards miniaturization of devices for energy production for portable electronics. Micro-combustors, when incorporated into a micro-power generation system, create the energy desired in the form of hot gases to power such technology. This creates the need for a design optimization of the micro-combustor in terms of geometry, fuel choice, and material selection. A total of five micro-combustor geometries, three fuels, and three materials were computationally simulated in different configurations in order to determine the optimal micro-combustor design for highest efficiency. Inlet velocity, equivalence ratio, and wall heat transfer coefficient were varied in order to test a comprehensive range of micro-combustor parameters. All simulations completed for the optimization study used ANSYS Fluent v16.1 and post-processing of the data was done in CFD Post v16.1. It was found that for lean, premixed fuel-air mixtures (φ = 0.6 - 0.9) ethane (C2H6) provided the highest flame temperatures when ignited within the micro-combustor geometries. An aluminum oxide converging micro-combustor burning ethane and air at an equivalence ratio of 0.9, an inlet velocity of 0.5 m/s, and heat transfer coefficient of 5 W/m2-K was found to produce the highest combustor efficiency, making it the optimal choice for a micro-combustor design. It is proposed that this geometry be experimentally and computationally investigated further in order to determine if additional optimization can be achieved.